Finds the bid with the minimal distance weightA*DeltaUtilA^2+weightB*DeltaUtilB^2
where DeltaUtilA is the difference between given utilA and the actual utility of the bid.
This method does a recursive depth-first search on the subtree that is rooted at the receiver, and returns
the first Objective or Issue with the given number.
Constructs an Enumeration of the entire subtree of the receiver (including itself) in preorder, containing only the
Issues, but not the normal Objectives.